1. Field of the Invention
The present invention relates to a pneumatic tire in which uniformity of the tire can be enhanced.
2. Description of the Related Art
A pneumatic tire is a complex comprising a combination of cord plies such as a carcass ply and a belt ply, and rubber components such as a tread rubber and a sidewall rubber such a tire is produced by incorporating these members to form a green tire, and by vulcanizing the green tire. However, non-uniformity is unavoidably generated in the green tire. This non-uniformity deteriorates the uniformity of a finished tire.
To enhance the uniformity of the tire, it is conventionally proposed to enhance the forming precision of each component. However, even if latest equipment of recent years is used, this method has a limitation in the enhancing effect.
Hence, the present inventors paid attention to the carcass which is a framework of the tire, and tried to enhance the uniformity. As illustrated in FIG. 4, a carcass ply “a” is formed through a primary ply c and a second ply f. The primary ply c includes a cord arrangement body b in which carcass cords are arranged in parallel to one another, and a topping rubber d for covering the cord arrangement body b.
The second ply f is formed by cutting the primary ply c into a plurality of pieces c1 having a predetermined size at a desired angle θ (about 75 to 90° in the case of a radial tire, and θ is 90° in the drawing) with respect to a length direction, and overlapping and jointing ends ce of the pieces c1 in succession. At that time, the pieces c1 are cut by length substantially equal to the width of the carcass ply “a”. Thereby, primary joined portions j1 that connected the pieces c1 are uniformly formed in the second ply f. Further, carcass cords are arranged in the second ply f at the angle θ with respect to the longitudinal direction X. The second ply f is cut into length corresponding to a radius of the tire, and is utilized as the carcass ply for forming a green tire.
A lowermost portion of FIG. 4 illustrates the carcass ply “a” wound around the forming former (not shown). Opposite ends fe, fe of the second ply f are spliced to each other so as to form a cylindrical shape which is continuous in the circumferential direction of the tire.
Here, the primary joint portion j1 appears substantially uniformly in the circumferential direction. However, the splice portion j2 with respect to the joint portion j1 is prone to be varied among tires. Especially in the case of a tire in which the primary joint portion j1 and the spliced portion j2 are close to each other, a lower component of the uniformity is deteriorated. This generates large vibration and noise at the time of high speed running.